Regulation of glomerulotubular balance. I. Impact of dopamine on flow-dependent transport

In response to volume expansion, locally generated dopamine decreases proximal tubule reabsorption by reducing both Na/H-exchanger 3 (NHE3) and Na-K-ATPase activity. We have previously demonstrated that mouse proximal tubules in vitro respond to changes in luminal flow with proportional changes in Na+ and HCO3− reabsorption and have suggested that this observation underlies glomerulotubular balance. In the present work, we investigate the impact of dopamine on the sensitivity of reabsorptive fluxes to changes in luminal flow. Mouse proximal tubules were microperfused in vitro at low and high flow rates, and volume and HCO3− reabsorption (Jv and JHCO3) were measured, while Na+ and Cl− reabsorption (JNa and JCl) were estimated. Raising luminal flow increased Jv, JNa, and JHCO3 but did not change JCl. Luminal dopamine did not change Jv, JNa, and JHCO3 at low flow rates but completely abolished the increments of Na+ absorption by flow and partially inhibited the flow-stimulated HCO3− absorption. The remaining flow-stimulated HCO3− absorption was completely abolished by bafilomycin. The DA1 receptor blocker SCH23390 and the PKA inhibitor H89 blocked the effect of exogenous dopamine and produced a two to threefold increase in the sensitivity of proximal Na+ reabsorption to luminal flow rate. Under the variety of perfusion conditions, changes in cell volume were small and did not always parallel changes in Na+ transport. We conclude that 1) dopamine inhibits flow-stimulated NHE3 activity by activation of the DA1 receptor via a PKA-mediated mechanism; 2) dopamine has no effect on flow-stimulated H-ATPase activity; 3) there is no evidence of flow stimulation of Cl− reabsorption; and 4) the impact of dopamine is a coordinated modulation of both luminal and peritubular Na+ transporters.

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Regulation of glomerulotubular balance. III. Implication of cytosolic calcium in flow-dependent proximal tubule transport

AJP Renal Physiology ◽

10.1152/ajprenal.00601.2014 ◽

2015 ◽

Vol 308 (8) ◽

pp. F839-F847 ◽

Cited By ~ 4

Author(s):

Zhaopeng Du ◽

Sheldon Weinbaum ◽

Alan M. Weinstein ◽

Tong Wang

Keyword(s):

Proximal Tubule ◽

Axial Flow ◽

Cytosolic Calcium ◽

Low Flow ◽

Angiotensin Ii Receptor ◽

Atpase Inhibitor ◽

Flow Effect ◽

Dependent Transport ◽

Glomerulotubular Balance

In the proximal tubule, axial flow (drag on brush-border microvilli) stimulates Na+ and HCO3− reabsorption by modulating both Na/H exchanger 3 (NHE3) and H-ATPase activity, a process critical to glomerulotubular balance. We have also demonstrated that blocking the angiotensin II receptor decreases baseline transport, but preserves the flow effect; dopamine leaves baseline fluxes intact, but abrogates the flow effect. In the current work, we provide evidence implicating cytosolic calcium in flow-dependent transport. Mouse proximal tubules were microperfused in vitro at perfusion rates of 5 and 20 nl/min, and reabsorption of fluid ( Jv) and HCO3− ( JHCO3) were measured. We examined the effect of high luminal Ca2+ (5 mM), 0 mM Ca2+, the Ca2+ chelator BAPTA-AM, the inositol 1,4,5-trisphosphate (IP3) receptor antagonist 2-aminoethoxydiphenyl borate (2-APB), and the Ca-ATPase inhibitor thapsigargin. In control tubules, increasing perfusion rate from 5 to 20 nl/min increased Jv by 62% and JHCO3 by 104%. With respect to Na+ reabsorption, high luminal Ca2+ decreased transport at low flow, but preserved the flow-induced increase; low luminal Ca2+ had little impact; both BAPTA and 2-APB had no effect on baseline flux, but abrogated the flow effect; thapsigargin decreased baseline flow, leaving the flow effect intact. With respect to HCO3− reabsorption, high luminal Ca2+ decreased transport at low flow and mildly diminished the flow-induced increase; low luminal Ca2+ had little impact; both BAPTA and 2-APB had no effect on baseline flux, but abrogated the flow effect. These data implicate IP3 receptor-mediated intracellular Ca2+ signaling as a critical step in transduction of microvillous drag to modulate Na+ and HCO3− transport.

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Regulation of glomerulotubular balance. II. Impact of angiotensin II on flow-dependent transport

AJP Renal Physiology ◽

10.1152/ajprenal.00277.2012 ◽

2012 ◽

Vol 303 (11) ◽

pp. F1507-F1516 ◽

Cited By ~ 13

Author(s):

Zhaopeng Du ◽

Laxiang Wan ◽

Qingshang Yan ◽

Sheldon Weinbaum ◽

Alan M. Weinstein ◽

...

Keyword(s):

Cell Volume ◽

Axial Flow ◽

Atpase Inhibitor ◽

Fractional Flow ◽

Cell Height ◽

Small Flow ◽

Dependent Transport ◽

The Impact ◽

Glomerulotubular Balance

Underlying glomerulotubular balance (GTB) is the impact of axial flow to regulate Na+ and HCO3− transport by modulating Na+-H+ exchanger 3 (NHE3) and H-ATPase activity. It is not known whether the cascade of events following a change in flow relies on local angiotensin (ANG II) generation or receptor availability. Mouse tubules were microperfused in vitro at flows of 5 and 20 nl/min, and net fluid (Jv) and HCO3− (JHCO3) absorption and cell height were measured. Na+ (JNa) and Cl− (JCl) absorption and changes in microvillous torque were estimated. Raising flow increased Na+ and HCO3− reabsorption but did not change either Cl− transport or cell volume. Losartan reduced absolute Na+ and HCO3− absorption at both low and high flows but did not affect fractional flow-stimulated transport. Compared with controls, in AT1a knockout (KO) mouse tubules, 53% of flow-stimulated Na+ absorption was abolished, but flow-stimulated HCO3− absorption was retained at similar levels. The remaining flow-stimulated JHCO3 was eliminated by the H-ATPase inhibitor bafilomycin. Inhibition of the AT2 receptor by PD123319 increased both JNa and JHCO3 but did not affect flow-mediated fractional changes. NHE3 expression at the protein level was reduced in AT1a KO mice kidneys. We conclude that 1) although the AT1a receptor is necessary for flow to impact NHE3, the effect on H+-ATPase is independent of AT1a; 2) the small flow-mediated changes in cell volume suggest a coordinate flow effect on both luminal and basolateral transporters; and 3) there is no evidence of flow-dependent Cl− transport, and thus no evidence for convective paracellular Cl− transport in mouse tubules.

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The impact of fresh gas flow on wash-in, wash-out time and gas consumption for sevoflurane and desflurane, comparing two anaesthesia machines, a test-lung study.

F1000Research ◽

10.12688/f1000research.13064.2 ◽

2017 ◽

Vol 6 ◽

pp. 1997 ◽

Cited By ~ 2

Author(s):

Fredrik Leijonhufvud ◽

Fredrik Jöneby ◽

Jan G. Jakobsson

Keyword(s):

Gas Flow ◽

Anaesthetic Agent ◽

Point Of View ◽

Low Flow ◽

Test Lung ◽

Minimal Alveolar Concentration ◽

Flow Rates ◽

Optimal Flow ◽

Gas Consumption ◽

The Impact

Low-flow anaesthesia is considered beneficial for the patient and the environment, and it is cost reducing due to reduced anaesthetic gas consumption. An initial high-flow to saturate the circle system ( wash-in) is desirable from a clinical point of view. We measured the wash-in and wash-out times (time to saturate and to eliminate the anaesthetic agent, AA), for sevoflurane and desflurane, in a test-lung with fixed 3 MAC vaporizer setting at different fresh gas flow (FGF) and calculated the consumption of AA. We tried to find an optimal flow rate for speed and gas consumption, comparing two anaesthesia machines (AMs): Aisys and Flow-i. Time to reach 1 minimal alveolar concentration (MAC) (wash-in) decreased (p<0.05) at higher flow rates (1 – 2 – 4) but plateaued at 4-4.8 l/min. The consumption of AA was at its lowest around 4-4.8 l/min (optimal flow) for all but the Aisys /desflurane group. Wash-out times decreased as FGF increased, until reaching plateau at FGF of 4-6 l/min. Aisys had generally shorter wash-in times at flow rates < 4 l/min as well as lower consumption of AA. At higher flow rates there were little difference between the AMs. The “optimal FGF” for wash-out, elimination of gas from the test-lung and circle system, plateaued with no increase in speed beyond 6 l/min. A fresh gas flow of 4 l/min. seems “optimal” taking speed to reach a 1 MAC ET and gas consumption into account during wash-in with a fixed 3 MAC vaporizer setting, and increasing fresh gas flow beyond 6 l/min does not seem to confirm major benefit during wash-out.

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In vitro estimation of the energy loss through turbulence in a porcine aortic valve stenosis model and silicone ascending aorta phantom using backlight particle tracking velocimetry

European Heart Journal ◽

10.1093/eurheartj/ehab724.0122 ◽

2021 ◽

Vol 42 (Supplement_1) ◽

Author(s):

M Chiarelli ◽

S F De Marchi ◽

D Obrist ◽

E Buffle

Keyword(s):

Left Ventricle ◽

Aortic Stenosis ◽

Energy Loss ◽

Particle Tracking Velocimetry ◽

Ascending Aorta ◽

Low Flow ◽

Mean Flow ◽

Flow Rates ◽

Stenosis Severity

Abstract Introduction Patients suffering from low-flow, low-gradient aortic stenosis present a decreased stroke volume due to decreased contraction or relaxation function of the left ventricle. As a low stroke volume tends to cause a low transvalvular flow, transvalvular pressure gradient (TVPG) and effective orifice area, the clinician cannot rely on those parameters with confidence for the evaluation of aortic stenosis severity. Hence new diagnostic parameters have to be developed. Energy loss through turbulence associated with aortic stenosis represented the wasted left ventricle work. Currently, echocardiographic measurement of the turbulence intensity is not validated for clinical evaluations of aortic stenosis. Methods Two porcine aortic valves were harvested and inserted in a flow loop that replicates the pulsatile flow of the heart. A stiffening of the valves was achieved by treating them with formaldehyde. The stiffening was externally confirmed by a custom-made force-displacement device quantifying the rigidity of the leaflet yielding two stiffness grades per valve. Each valve was tested under three different mean flow rates (1, 2.5, and 4 l/min) at each of the two stiffness grades. Moreover the pressure in the left ventricle chamber and in the aortic chamber was recorded to calculate the TVPG. Particle tracking velocimetry measurements into the transparent silicone ascending aorta phantom allowed the computation of the turbulent kinetic energy (TKE), to evaluate the energy loss due to turbulence. Results We could confirm the enhanced rigidity of the valve leaflets with our custom device (data not shown) and measure a consistent increase in TVPG across all mean flow rates between the two stiffness grades. Moreover, an explicit increase of the TKE in the aortic phantom could be measured after the stiffening process (73.1% under 1 l/min, and 43% under both 2.5 and 4 l/min). In addition, a good correlation (R = 0.86) between the mean TVPG and the TKE was found. Conclusions This project demonstrated the possibility of quantifying the energy loss attributed to turbulence for porcine valves in vitro for native and added stiffness grade. This project lays the foundation for the development of a new diagnostic tool for the assessment of stenosis severity in patients with low-flow, low-gradient aortic stenosis in cardiac imaging tool such as echocardiography. FUNDunding Acknowledgement Type of funding sources: None. TVPG and its correlation with TKE Intensity graphs of the TKE

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Alternative Splicing of FN (Fibronectin) Regulates the Composition of the Arterial Wall Under Low Flow

Arteriosclerosis Thrombosis and Vascular Biology ◽

10.1161/atvbaha.120.314013 ◽

2020 ◽

Author(s):

Patrick A. Murphy ◽

Noor Jailkhani ◽

Sarah-Anne Nicholas ◽

Amanda M. Del Rosario ◽

Jeremy L. Balsbaugh ◽

...

Keyword(s):

Extracellular Matrix ◽

Alternative Splicing ◽

Low Flow ◽

Matrix Composition ◽

Splice Isoforms ◽

Vitro Assay ◽

Disturbed Flow ◽

The Impact

Objective: Exposure of the arterial endothelium to low and disturbed flow is a risk factor for the erosion and rupture of atherosclerotic plaques and aneurysms. Circulating and locally produced proteins are known to contribute to an altered composition of the extracellular matrix at the site of lesions, and to contribute to inflammatory processes within the lesions. We have previously shown that alternative splicing of FN (fibronectin) protects against flow-induced hemorrhage. However, the impact of alternative splicing of FN on extracellular matrix composition remains unknown. Approach and Results: Here, we perform quantitative proteomic analysis of the matrisome of murine carotid arteries in mice deficient in the production of FN splice isoforms containing alternative exons EIIIA and EIIIB (FN-EIIIAB null) after exposure to low and disturbed flow in vivo. We also examine serum-derived and endothelial-cell contributions to the matrisome in a simplified in vitro system. We found flow-induced differences in the carotid artery matrisome that were impaired in FN-EIIIAB null mice. One of the most interesting differences was reduced recruitment of FBLN1 (fibulin-1), abundant in blood and not locally produced in the intima. This defect was validated in our in vitro assay, where FBLN1 recruitment from serum was impaired by the absence of these alternatively spliced segments. Conclusions: Our results reveal the extent of the dynamic alterations in the matrisome in the acute response to low and disturbed flow and show how changes in the splicing of FN, a common response in vascular inflammation and remodeling, can affect matrix composition.

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4-[1-ethyl-1-methylhexy]-phenol Induces Apoptosis and Interrupts Ca2+ Homeostasis via ROS Pathway in Sertoli TM4 cells

10.21203/rs.3.rs-542558/v1 ◽

2021 ◽

Author(s):

Xiaozhen Liu ◽

Fuxiang Li ◽

Zhaoliang Zhu ◽

Gaoyi Peng ◽

Danfei Huang ◽

...

Keyword(s):

Oxidative Stress ◽

Atpase Activity ◽

Chain Structure ◽

Side Chain ◽

Ros Generation ◽

Intracellular Ca ◽

Ros Scavenger ◽

Induced Apoptosis ◽

The Impact

Abstract Biological effect of an individual nonylphenol (NP) isomer extremely relies upon the side chain structure. This research was designed to evaluate the impact of NP isomer, 4-[1-ethyl-1-methylhexy]-phenol (NP65), on Sertoli cells in vitro. Sertoli TM4 cells were exposed to various concentration (0, 0.1, 1, 10, or 20 μM) of NP65 for 24 h, and the outcomes indicated that treatment of NP65 induced reactive oxygen species (ROS) generation, oxidative stress as well as apoptosis for Sertoli TM4 cells. In addition, it was found that NP65 exposure affected homeostasis of Ca2+ in Sertoli TM4 cells by increasing cytoplasm [Ca2+]i, inhibiting Ca2+-ATPase activity and decreasing cAMP concentration. Pretreatment with ROS scavenger, N-acetylcysteine (NAC), attenuated NP65-induced oxidative stress as well as apoptosis for TM4 cells. Furthermore, NAC blocked NP65-induced disorders of Ca2+ homeostasis by attenuating the growth of intracellular [Ca2+]i and the inhibition of Ca2+-ATPase and cAMP activities. Thus, we have demonstrated that NP65 induced apoptosis as well as acted as a potent inhibitor of Ca2+-ATPase activity and resulted in disorder of Ca2+ homeostasis in Sertoli TM4 cells, ROS participated in the process. Our results supported the view that oxidative stress acted an essential role within the development of apoptosis and Ca2+ overload in TM4 cells as a consequence of NP65 stimulation.

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Effect of parathyroid hormone on bicarbonate absorption by proximal tubules in vitro

AJP Renal Physiology ◽

10.1152/ajprenal.1979.236.4.f387 ◽

1979 ◽

Vol 236 (4) ◽

pp. F387-F391 ◽

Cited By ~ 1

Author(s):

Y. Iino ◽

M. B. Burg

Keyword(s):

Steady State ◽

Parathyroid Hormone ◽

Proximal Tubules ◽

Renal Tubules ◽

Bicarbonate Concentration ◽

Flow Rates ◽

Straight Tubules ◽

Convoluted Tubules ◽

Tubule Fluid

The effect of parathyroid hormone on bicarbonate absorption was tested in rabbit proximal renal tubules perfused in vitro. In proximal straight tubules 0.05 U/ml of parathyroid hormone caused a large and reversible increase in the steady-state bicarbonate concentration in tubule fluid. Further, the rates of bicarbonate and fluid absorption (measured at faster flow rates) were inhibited approximately 50% by the hormone. We conclude that parathyroid hormone directly inhibits fluid and bicarbonate absorption by proximal straight tubules, causing an increase in the bicarbonate concentration in the tubule fluid, and we suggest that this action of the hormone contributes to the increase in renal bicarbonate excretion that is generally caused by the hormone. In proximal convoluted tubules, parathyroid hormone was previously demonstrated by other investigators to inhibit fluid and bicarbonate absorption approximately proportionally, so that there was little or no change in the bicarbonate concentration in tubule fluid. In agreement we found in the present studies that 0.05 U/ml of the hormone did not affect the steady-state bicarbonate concentration in proximal convoluted tubule fluid and that 5 U/ml caused only an equivocal increase in tubule fluid bicarbonate concentration.

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Lactate absorption in Thamnophis proximal tubule: transport versus metabolism

AJP Renal Physiology ◽

10.1152/ajprenal.1980.238.3.f218 ◽

1980 ◽

Vol 238 (3) ◽

pp. F218-F228 ◽

Cited By ~ 1

Author(s):

P. H. Brand ◽

R. S. Stansbury

Keyword(s):

Proximal Tubule ◽

Lactate Concentration ◽

Flux Ratio ◽

Proximal Tubules ◽

Chemical Gradient ◽

Flow Rates ◽

Net Flux ◽

Unidirectional Fluxes ◽

Absorptive Flux

Proximal tubules from the kidney of Thamnophis (garter snake) were perfused in vitro and unidirectional fluxes of lactate measured using L(+)-[U-14C]lactate, (lactate concentration, 1 mM). The lumen-to-bath (absorptive) flux (Jlb lact) significantly exceeded the bath-to-lumen flux (backflux) (Jbl lact) in each of 12 tubules (seven distal proximal and five proximal proximal). The flux ratio (Jlb lact/Jbl lact) was approximately 3.00. At flow rates of 13-16 nl/min and lactate concentration of 1 mM the net flux was about 1.60 pmol . min-1 . mm-1 in both proximal proximal and distal proximal segments. Both fluxes were decreased by perfusion at 5 degrees C. To determin e the contribution of metabolism of lactate to its absorption, Jlb lact was measured at 25 degrees C in 10 distal proximal tubules during perfusion with [14C]lactate, lactate concentration, 1 mM, and with [methoxy-3H]inulin. In these experiments, the amount of 14C found in the bath was 93% of the amount of 14C absorbed from the lumen. Chromatography showed that all of the 14C found in the bath was [14C]lactate. These data establish that in Thamnophis proximal tubule lactate absorption occurs against an electro chemical gradient by transport of the intact lactate molecule without significant metabolism.

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In Vitro Perfusion of Hybrid Artificial Pancreas Devices at Low Flow Rates

ASAIO Journal ◽

10.1097/00002480-199207000-00073 ◽

1992 ◽

Vol 38 (3) ◽

pp. M443-M449 ◽

Cited By ~ 2

Author(s):

CARLOS A. RAMÍREZ ◽

MILDRED LÓPEZ ◽

CONNIE L. STEPHENS

Keyword(s):

Artificial Pancreas ◽

Low Flow ◽

In Vitro Perfusion ◽

Flow Rates

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Impact of Parylene Coating On Heating Performance of Intravenous Fluid Warmer: A Bench Study

10.21203/rs.3.rs-970986/v1 ◽

2021 ◽

Author(s):

Danielle K. Bayoro ◽

Herman Groepenhoff ◽

Daniel Hoolihan ◽

Edward A. Rose ◽

Michael J. Pedro ◽

...

Keyword(s):

Perioperative Complications ◽

Age Groups ◽

Intravenous Fluid ◽

Low Flow ◽

Fluid Temperature ◽

Target Temperature ◽

Flow Rates ◽

Fluid Warmer ◽

Increased Risk ◽

The Impact

Abstract Background Perioperative hypothermia is a common occurrence, particularly with the elderly and pediatric age groups. Hypothermia is associated with an increased risk of perioperative complications. One method of preventing hypothermia is warming the infused fluids given during surgery. The enFlow™ intravenous fluid warmer has recently been reintroduced with a parylene coating on its heating blocks. In this paper, we evaluated the impact of the parylene coating on the new enFlow’s fluid warming capacity. Methods Six coated and six uncoated enFlow cartridges were used. A solution of 10% propylene glycol and 90% distilled H2O was infused into each heating cartridge at flow rates of 2, 10, 50, 150, and 200 ml/min. The infused fluid temperature was set at 4°C, 20°C, and 37°C. Output temperature was recorded at each level. Data for analysis was derived from 18 runs at each flow rate (six cartridges at three temperatures). Results The parylene coated fluid warming cartridge delivered very stable output of 40°C temperatures at flow rates of 2, 10, and 50 ml/min regardless of the temperature of the infusate. At higher flow rates, the cartridges were not able to achieve the target temperature with the colder fluid. Both cartridges performed with similar efficacy across all flow rates at all temperatures. Conclusions At low flow rates, the parylene coated enFlow cartridges was comparable to the original uncoated cartridges. At higher flow rates, the coated and uncoated cartridges were not able to achieve the target temperature. The parylene coating on the aluminum heating blocks of the new enFlow intravenous fluid warmer does not negatively affect its performance compared to the uncoated model.

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